Researchers from University of Geneva in Switzerland and University of Oxford in the UK examined 29 years' worth of data collected from 6,203 adults who ranged in age from 41 to 96 years old when they began the study.

The tasks - all well-established measures of cognitive ability, were administered up to four times over a 12-year period, allowing researchers to assess participants' baseline performance and change in performance over time for each domain.

To gauge participants' health, researchers used the Cornell Medical Index, a measure that includes detailed checklists of a total of 195 pathological symptoms related to physical and psychological disorders.

Finally, the researchers looked at participants' subjective reports of various lifestyle factors, including perceived health, number of prescribed medicines, sleep patterns, hobbies, leisure activities, and social interactions.

Using two types of statistical analysis, researchers were able to assess the relative importance of a total of 65 different variables in predicting participants' mortality risk.